Tube tester?

I'll add that you can get a lot of info about a tube from your amp, especially is it has manual bias adjust.  Not everything, but a lot.

you have to understand the electronics though.

Jerry

Like a broken record, I keep on saying anyone with tube equipment should buy their own tube tester.

I had a nice 666 Eico tester. I didn't use it much. I buy new production tubes from very reliable sources and I have only had one issue with a noisy preamp tube. The tube tester doesn't insure quiet tubes because it's the function of the preamp circuit that determines that. Listening is the only way sometimes. I've also blown power tubes, that is spectacular and no measurements are needed, the whole tube bank gets replaced at that point. Bottom line...I have no tester and really not missing it.  

"95/91 or 46/41" If these numbers are written on the side of a tube with a Sharpie they are the test results of a 2 section tube. Unfortunately they are meaningless unless the tube tester is known along with the results chart. Now generally 95/91 is generally a good reading, however 46/41 is not. Take this with a grain of salt as the tube tester is unknown. Always buy tubes, especially ones that need matching from a reputable vender. A Google search will give you a start.

Check craigslist, they typically aren't too much money there and they almost always seem to have.  Years ago, every hardware and drugstore had one.  You'd take your tubes in a grocery bag and plug away.  I do not have one.  I listen and if something is off, I swap the whole set for said device.  If you test and find a bad one, a new one will not match up with the old ones. 

I bought a tube tester when I started playing with DHT and rectifiers.     Having one actually saved my new amp from a shorted rectifier.   It was a NOS 5r4gy from 1956 that I bought as a group of 4.  They were time capsule condition yet one was bad

Your best bet is to pay a few bucks extra to have pairs and quads matched.   Also a good idea to have dual triodes matched and screened for noise.   My best quality tube sets have been purchased from trusted sources that match.    This was proven after testing a bunch of tubes collected over the years

When I receive them I also test them. 

I was lucky, I bought a mint Hickok that works great and is accurate with several "bogey" tubes so it's more than accurate for weeding out bad tubes and matching good ones.    MOST TUBE TESTERS NEED WORK.    Always remember that if thinking of getting one.   

Almost all of my gear has tubes so for me it is peace of mind. 

It is rare to find one this nice that works so use caution if looking for one.  Best to just buy from vendors with an Amplitrex or similar computerized test equipment.